SPEC continues to offer service support in dismantling and erection of concrete batching plants and mixers, in addition to offering concrete mix design.
REBOUND HAMMER TEST (RHT)
If the strength of concrete is high, then the rebound number/value is also high. Rebound hammers are available with different impact energy. The lowest energy rebound hammer (0.07 kgm) is being used for testing light weight concrete, the medium energy ( 0.09 kg-m ) is being used for normal weight concrete, and the high impact energy (3.0 kg-m) is used for testing concrete pavements / runways, etc.,
The working principle of the Rebound hammer is very simple. When a spring loaded weight with a shaft is pressed against the concrete surface from its initial protruded position (rider reading `Zero‟ on the scale provided on the hammer), the weight falls on the surface and rebounds carrying a rider along with it over the calibrated scale depending on the surface strength.
ULTRASONIC PULSE VELOCITY TEST
Ultrasonic Pulse velocity test using ultrasonic tester (in this case, TICO Tester, Fig.) gives information on the integrity of concrete in the interior portions of concrete in the member.
The presence of cracks, voids and other imperfections, changes in the structure of concrete, that occur with time, and the present quality of the concrete in relation to standard requirements could be determined from this test.
Values of elastic modulus of concrete can also be determined by using the UPV values.
(i) Direct method
This method will give maximum sensitivity and provide a well-defined path length. This method is adopted when the opposite sides of a member/structure are available for scanning.
(ii) Semi-direct method
Sometimes it may be required to examine the concrete by using diagonal paths, it is here semi-direct method is suitable.
(iii) Indirect method
The indirect method is useful, when the opposite surfaces of the member/structure are not accessible.
Non-Destructive test results along with the compressive strength values obtained on the core samples extracted randomly, from the structural member (in question) will normally give best assessment on the quality, and insitu strength of the concrete.
Considering this, core locations in the concrete components are to be identified and marked on the member in the building at random for extraction of cores and testing as per the standard practice. In some places it is not possible to avoid the rebar. Suitable correction for its presence can be effected in calculating the strength.
Core samples are extracted using core drilling machine, for evaluating the compressive strength. Normally, core diameter is decided based on the size of the aggregate. The minimum dia of the core should be 3 times the maximum size of aggregate used in the concrete. It is the practice to specify 100 mm dia. as minimum as the results obtained are closer to the standard cylinder (150mm.dia x 300mm length).
In case it is not possible from other considerations, lower diameters can be extracted. It is always better to extract without cutting the reinforcements. In case it is cut, and present in the body of the core, there is empirical formula suggested in BS 6089:1981.
Soil Stabilization using lime is an established practice to improve the characteristics of fine grained soils especially those soils having high clay – content.
Lime is a excellent solution for soil modification and stabilization. . Using lime can substantially increase the stability and load-bearing capacity of the sub grade.
Soil profile can be improved by the addition of lime which reacts with clay soil to form hydrated cementitious compounds that increases the stability of the soil.
Lime when added undergoes multiple reaction in which the main reaction includes - Flocculation, Cation – exchange and pozzolanic reaction which results in changing the properties of soil desirably.
Lime piles are installed at definite intervals specific to varying site conditions
The lime slurry once injected into the bored holes shall fill through the crevices in the soil subgrade.
The lime reacts with present aluminates and silicates to form hydrated pozzolanic compounds which results in improvement of soil bearing characteristics.
The key to soil stabilization is a reactive soil, a good mix design protocol, and reliable construction practices.